The present invention concerns a method for eliminating interference in measuring signals which are corrupted by pulsed interference signals having a known or determinable interference pulse interval, whereby the detection period of an individual measured value is shorter than one interference pulse period, and a plurality of individual measured values is detected at freely selectable time intervals of the measuring signal.
The approach usually taken when external sources of interference are present, i.e., to shield the affected lines, sensors or circuit parts, is frequently associated with considerable costs and is often ineffective, in particular when magnetic coupling occurs. Frequently, shielding cannot be realized, due to the principle involved. This is the case, for example, with capacitance-based positioning devices, e.g., to locate dielectric inclusions in construction materials (also referred to occasionally as stud finders). In this case, the plates of the precision capacitor of the sensor cannot be shielded, due to the principle involved. Positioning devices of this type that are particularly susceptible to interference are described in publications WO 02/14847 A1 and DE 199 15 016 C2, for example.
Other devices that are also particularly susceptible to interference are radar devices, radio devices and other applications, with which high-frequency interferences cannot be shielded, due to the principle involved.
A further, often-used method which results in interference reduction using averaging often results in unacceptably long measurement times. The interference amplitude drops only with the square root of the measurement time.
If a utilized working frequency of the measuring system is in the GHz range, e.g., between 1 and 3 GHz, there is considerable potential for interference by various mobile communication applications, e.g., by applications based on the DECT, GSM and Bluetooth standards. Radio-interference sources of this type, which function according to “TDMA” technology, transmit pulsed interference signals at periodic intervals (frames) only for a short period (time slots), the interference signals resulting in a periodic interference of the received measuring signal.
Measuring devices which do not operate in the GHz range are often also influenced, however. For example, non-linear characteristic curves of electronic components in measurement circuits in combination with high transmitting power of cellular telephones, for example, also cause interference in circuits which actually operate only in the low-frequency range. The method according to the present invention results in success in these cases as well.
In general, the effects of pulsed sources of interference are observed in diverse types of measuring devices in which weak electrical measured quantities are detected. The corruption of measuring signals can be caused by electromagnetic interference, in particular, which can occur in measurement sensors and evaluation circuits, for example.
The present invention is based on the object of providing a method of the type mentioned in the preamble, with which interference is eliminated as effectively as possible from a measuring signal disturbed by a pulsed, periodic interference signal.